We have been studying the role that protein degradation plays in regulating cell growth control, through the study of mutants defective in ATP-dependent protein turnover. E. coli lon mutants are defective in cell division regulation after DNA damage, and we have previously demonstrated that this defect is due to stabilization of the highly unstable cell division inhibitor, SulA. lon mutants also overproduce capsular polysaccharide; we have identified an unstable positive regulator of capsule synthesis, RcsA, which is stabilized in lon mutants. The sequence of the rcsA gene shows no striking similarities to other lon substrates. rcsA-lac fusions which we have isolated will allow us to examine the transcriptional and translational control of this gene. Using cells devoid of lon activity, we have biochemically identified a novel two-component, ATP-dependent protease. Using amino acid sequence data from one of the purified components, plasmids carrying the gene are being identified. Using genetic screens, we have also identified and partially mapped a function which is capable of substituting for lon, and presumably codes for another protease with potential regulatory functions in E. coli.
